1. Field of the Invention
The present invention relates to electronic components and methods for manufacturing the electronic components, and more particularly, to an electronic component including outer electrodes made of conductive paste and a method for manufacturing the electronic component.
2. Description of the Related Art
Japanese Unexamined Patent Application Publication No. 2006-351727, for example, describes an interesting technology related to the present invention. Japanese Unexamined Patent Application Publication No. 2006-351727 describes a method for manufacturing a high-reliability electronic component in which outer electrodes have a sufficient thickness at corner portions and ridge portions of end surfaces of an electronic component element, and in which the outer electrodes have a uniform and appropriate thickness in central regions of the end surfaces.
In this method, conductive paste is applied to an end surface of the electronic component element in a first conductive-paste-applying step. After that, the end surface of the electronic component element to which the conductive paste is applied is pressed against a flat surface having no conductive paste applied thereto, and is then moved away from the flat surface, so that the conductive paste applied to portions other than the corner portions and the ridge portions of the end surface is removed. Next, the end surface of the electronic component element is dipped into the conductive paste in a second conductive-paste-applying step, so that the conductive paste is applied to the end surface over the entire area thereof. After that, the end surface of the electronic component element to which the conductive paste is applied is pressed against an excess-conductive-paste-removing surface, which has projections and recesses, and is then moved away from the excess-conductive-paste-removing surface, so that an excess portion, including a bulging portion, of the conductive paste applied to the end surface is removed.
Japanese Unexamined Patent Application Publication No. 2006-351727 describes that, according to the above-described method for manufacturing an electronic component, outer electrodes can be formed so as to have a sufficient thickness at ridge portions, and a high-reliability electronic component can be manufactured.
A problem to be solved by preferred embodiments of the present invention will be described with reference to a monolithic ceramic capacitor, which is an example of an electronic component.
To satisfy an increasing demand for large-capacitance monolithic ceramic capacitors, it is necessary to increase the volume capacitance rate. Various measures for increasing the volume capacitance rate have been studied. An example of such a measure is to reduce the volume of outer electrodes to increase the volume capacitance rate.
To increase the volume capacitance rate by reducing the volume of the outer electrodes, it is necessary to reduce the thickness of the outer electrodes. However, when the thickness of the outer electrodes, which are made of conductive paste, is reduced, even if the thickness of the outer electrodes is sufficient on the end surfaces of a component body, the thickness may be insufficient on the ridge portions of the component body. This may lead to a reduction in moisture resistance of the electronic component. For example, when the outer electrodes are subjected to wet plating, plating solution may intrude into the spaces between the component body and the outer electrodes and the inner space of the component body through portions of the outer electrodes on the ridge portions of the component body. The intrusion of the plating solution may cause a solder explosion in a process of mounting the monolithic ceramic capacitor with solder.
In addition, to reduce the thickness of the outer electrodes made of conductive paste, it is necessary to use a conductive paste having a low viscosity. However, when an end surface of the component body is dipped into the conductive paste having a low viscosity, the conductive paste easily spreads upward along side surfaces of the component body. FIG. 13 shows an electronic component 1 in which outer electrodes 3 and 4 are formed on both end portions of a component body 2. When the conductive paste used to form the outer electrodes 3 and 4 has a low viscosity, the conductive paste easily spreads upward along side surfaces 5 of the component body 2. Therefore, as illustrated in FIG. 13, the outer electrodes 3 and 4 tend to be formed such that central portions of edges 6 and 7 thereof on the side surfaces 5 are curved so as to bulge by a relatively large amount.
The fact that the outer electrodes 3 and 4 have the curved edges 6 and 7, respectively, as described above does not cause a serious problem. However, when attention is focused on the amounts by which the curved edges 6 and 7 of the outer electrodes 3 and 4 bulge, as the amounts of bulge increase, the difference between the amount of bulge of the edge 6 of one outer electrode 3 and that of the edge 7 of the other outer electrode 4 increases. In FIG. 13, the amounts of bulge of the curved edges 6 and 7 of the outer electrodes 3 and 4, respectively, drawn by solid lines are substantially the same. However, the amount of bulge of the edge 7 of the outer electrode 4 drawn by the broken line is greater than that of the curved edge 6 of the outer electrode 3 drawn by the solid line.
As in the case of the edge 7 of the outer electrode 4 drawn by the broken line in FIG. 13, when the amount of bulge of the edge 7 of the outer electrode 4 differs from that of the edge 6 of the outer electrode 3 that opposes the edge 7 of the outer electrode 4, solder adheres to the outer electrodes 3 and 4 in different manners in the process of mounting the electronic component 1. As a result, a phenomenon called tombstoning may occur.